AAprilia rear suspension

[Sliding Pillar]

 William, from the excellent publication by Lancia to celebrate the Aprilia's 50th anniversary the colours are listed as follows:-
Model 238 (1st series) Grigio, Blu, Nero, Granada, Verde, also for Lusso model colours Metallic (although not stated what colours!)
Model 239 (Chassis) Blu Lancia, Grigio chiaro, Beige chiaro.
Model 438 (2nd series) Grigio metallic, Blu, Nero, Beige, Verde, Bruno chiaro, Metallic scuro, Bruno, Blu metallic, Grigio acciaio, Grigio chiaro, Nocciola, Beige, Amaranto.
Model 439 (2nd series chassis) grigio metallic, Blu.
There is also a full list of which interior colour matches the paint colour, but if I include all of these I will be here all night!!
Regards Ade.

[Scarpia]

gosh! (does anybody still say gosh?), i didn't expect such a range of choice and perhaps shortsightedly, I always thought the metallic ones I saw were not original colours...

what form of publication is this that you refer to Ade, leaflet, book, magazine?

[Sliding Pillar]

It is a soft bound Book/magazine produced by the Lancia Club with help from Lancia with a collection of articals and technical data, 60 pages, silver cover with 'Aprilia' and Lancia logo on the front. Mine was sent to me from Lancia when I enquired about details of my Aprilia in about 1988, I've not seen another..........and this one is NOT for sale!!!!!!

[Scarpia]

And I was going to offer 25000 pounds.......

[ben]

   The book Ade has sounds intregueing. I have the same data in a 44 page booklet called the LMC Journal for spring 1969.There is a John Maltby photo of a standad Aprilia on the front.Editor at that time was Nigel Trow.Text is in english!
   Going back to rear suspension matters I previously suggested that employing the transverse leaf spring enabled the aprilia designers to use much softer torsion bars.I have now measured up the various components and made some first order estimates, using very basic theory, of the actual spring rates.
   I found that the leaf spring has a rate of about 145 lb/in (loaded in the centre and supported at the ends).Because of the leverage effect due to  the connection points, via the cables, being about half way along the trailing arms,when installed in the car this gives an overall stiffness for the back end (bounce stiffness) of only 43 lb/in.
   My calcs. show that the torsion bars give a much higher rate of bounce stiffness, viz. 317 lb/in, i.e. 7.5 times stiffer than the leaf. Total rear end bounce stiffness is thus 43+317=  360 lb/in.---(It is a good job I am not a green-grocer or I could be arrested for using these Imperial units)----If 360 lb/in was the design target the torsion bars on their own would only need to be 14% stiffer, i.e. 4.5% thicker,which is a somewhat smaller difference than I expected.
   Checking with the drivers handbook confirms that the system is set up "by the factory" with the bars in a neutral state, although it is not specified what weight the car should be carrying. Experience seems to show it should be well loaded. Thus when travelling light the bars and the leaf are working in opposition but when load is increased the torsion bars go through the neutral position and then start assisting with the load carrying as previously described. It is certainly true that with this system the stress level in the torsion bars is very much lower than would be the case if they were carrying all the weight.
It would be an interesting experiament to set up the rear end of the car without the transverse spring and see how it behaved. Because they are so stiff it would only be necessary to set the bars around by 17 degrees (two splines at the inner ends.There are 42 and 48 at the outboard end to give the vernier ajustment capability referred to by Colin M. They can be set to within approx. one degree which gives a variation in ride height of about 1/6" or 4 mm.)
   Incidentally Colin I am allmost certain that the Light 15 Citroen rear torsion bars are anchored in the middle. I know the fronts were longer and ran longitudinally and as you say  Renaults ran the full width at the back---giving rise to unequal wheelbase distances between the two sides on the R16 and R4 and maybe others-----something I am sure Vincenzo would never have countenanced! With short bars it is easy enough to get the required spring rate but at the penalty of high stress levels.
   Overall however the excellent handling of the Aprilia is I am sure down to the well engineered wheel location rather than the choice of springing.
   Finally (if you are still awake!) --with reference to D.W.'s observation of a slight list to port when his nearside cable broke---in this state most of the near-side weight of the car is still supported by the spring which is now bearing down directly onto the road.It has to move down about 8" before striking the road but even after this degree of "relaxation" it is still loaded enough to support the car. Acting directly the force onto the road is roughly double what it is when acting through the road wheel via the leverage system of the swing arm.

[davidwheeler]

...except that the spring was not resting on the road, it was hanging on the end of the friction shock absorber and so still attached to the car but the lower end displaced by about 6 inches.  When I replaced the cables I had the springs tied to the torsion bars by nylon tapes and the attitude of the car was much as usual despite the tapes stretching to, again, some 4 to 6 inches displacement.  All is well now!

[ben]

   I had not picked up on that mod which I am sure saved you quite a bit of grief. The standard attachment point for the shock-absorber arm is directly onto the suspension trailing arm just below the bump stop platform.
  It is interesting that we now have two instances of rear suspension cable breakage reported on this forum and in neither case did the legendary barrel-roll occur. I wonder if your car was deiberately modified to avoid this.
  Glad all is well now.

[ben]

   Me again!   Two further points of clarification.

                1.   Re-reading Colins latest thoughts the re-assembly procedure that requires the boot to be loaded to reach the neutral position of the torsion bars involves installing the leaf spring first. The load is to compress the leaf, with the wheels on the ground, and then the bars are rotated to find the position where they will just slide in.
                     If the bars were inserted first one would need to know precisely what angle to set the trailing arms to in their free state before inserting the bars. The leaf spring could then be fitted (using the special clamp) without having to load up the car.

               2.   With the leaf spring trapped by the shock-absorber as I now understand was the case for DW's cable failure the spring load is "locked in" and that side of the car is fully supported by the torsion bar alone. The modest list he observed shows the capability of the torsion bar if it is put to the task.

[davidwheeler]

I actually had a choice of two possible mountings.  As my hydraulic mediated shockers which mounted on the side were perished I fitted the dry ones which mount to the end of the spring.  Lucky!!

[ColinMarr]

Ben,

I think I explained it badly. The assembly operation I was recalling was with a fully relaxed transverse spring – like it was a semicircle. This required me to raise the rear of the car high off the ground with blocks under the sills. Before offering up the spring the angle of the trailing arms were set by reference to datum marks. I forget what these were, but there was a measure whereby the arms (without the bars) were set to some set position so that the distance from the top of the hub flange to some point under the rear wing ( I half remember a ‘blue plate’ with a simple horizontal line on it!) was set and equal both sides. Then the bars were fitted, using the vernier options to get the best fit.

Then it was a matter of jacking up one end of the leaf spring at a time to get it to a point where the end fittings, with the cables could be bolted in. This was the point at which I contemplated getting mother-in-law to climb into the rear seat, which was of course very high off the ground – hence the better option of paving slabs in the boot. And this is why the absence of trolley jacks, which we all take for granted now, made it all a bit more problematic.

Happy and innocent days!

Colin       

[Scarpia]

with the car perched precariously in the air on blocks and jacks and using the spring compressor tool referred to as Colin describes .With the bars inserted you need to place the trailing arms at an angle so the distance from the top of the hub disk to a projected line from the damper mounting bolts is 165 mm. This requires no family ballast or other relative contributions of course...
i'll post a drawing if this is unclear.